Conventionally, as shown in FIG. 12, various heavy-load tires having a so-called wind bead structure in which a turned-up portion b2 of a carcass ply b is wound around a bead core c have been proposed. Such a heavy-load tire can prevent damages arising from an end portion of the turned-up portion b2 because the end portion of the turned-up portion b2 is disposed near the bead core c, which is less susceptible to distortion during driving. As a result, such a heavy-load tire has an outstanding advantage in that the bead durability can be improved.
With the wind bead structure, the bead deformation at the time of grounding is relatively large as compared with a conventional non-wind bead structure. Therefore, a bead reinforcing layer f becomes necessary which has a reinforcing cord such as a steel cord and which reinforces a bead portion by being turned up around the bead portion into a U shape.